Genotoxic Disinfection By-products Research Articles

Formation of halonitromethanes from glycine during LED-UV265/chlorine disinfection

LED-UV265/chlorine is a promising alternative disinfection technology that emits mono-wavelength light for high germicidal efficiency. Halonitromethanes (HNMs) are highly cytotoxic and genotoxic disinfection byproducts that can be formed during LED-UV265/chlorine disinfection. Thus, this work aimed to investigate the HNMs formation from glycine (Gly) during LED-UV265/chlorine disinfection. The results indicated that the concentrations of chlorinated-HNMs (Cl-HNMs) increased first and then decreased as the reaction proceeded. Besides, the effects of operating parameters (UV intensity, free chlorine dosage, and pH) and coexisting ions (Cu2+ and Br−) on HNMs formation were investigated. It was found that the formation concentrations of Cl-HNMs increased with the increase of LED-UV265 intensity and free chlorine dosage but decreased with increased pH. The presence of Cu2+ promoted the formation of Cl-HNMs. The total concentration of HNMs (at 3 min) with adding 1.5 mg/L Cu2+ was 30.90% higher than that without Cu2+. Notably, nine species of HNMs were detected after adding Br−, and the total concentrations of HNMs were enhanced. Moreover, Cl-HNMs were gradually transformed into brominated (chlorinated)-HNMs and brominated-HNMs as Br− concentration increased. According to the findings, the possible formation mechanism of HNMs from Gly during LED-UV265/chlorine disinfection was deduced. Finally, it was demonstrated that the formation laws of HNMs from Gly in real water samples were basically consistent with those in simulated water. Insights obtained in this study help to comprehend the HNMs formation from Gly and provide strategies for controlling the production of HNMs during LED-UV265/chlorine disinfection.

Genotoxicity and Health Risk of Seawater Desalination Based on Reverse Osmosis: A Case Study of Two Seawater Desalination Plants in Zhoushan, China

Typically, the shortage of freshwater will limit the social and economic development of island regions. As a non-conventional, high-quality water source, desalinated seawater can be incorporated into the urban water supply system. The genotoxicity of disinfection by-products in drinking water was always viewed as a concern for human health. However, only a few studies were conducted based on this issue of desalinated seawater. In this study, the comet assay was conducted to investigate the genotoxicity caused by organic extracts in the specific drinking water produced in two full-scale desalinated seawater purification plants from the Zhoushan Islands in eastern China. The water samples were collected from four different locations along the treatment train in the plants. The quality of desalinated seawater conformed to the national standards for drinking water in China, except for the higher boron content. The results of the comet assay showed that all the organic extracts from the water samples were able to induce different levels of DNA damage on HL-60 cells (K finished water = 6.635 and 7.698, respectively). Compared with that from the water plants with fresh source water, the genotoxicity of the finished water of the seawater desalination plant was determined to be the lowest. The correlations between desalinated seawater consumption and two important chronic diseases, namely hypertension and coronary heart disease, could not be supported by the current data of epidemiological investigation. These results demonstrate the genotoxicity of the desalinated seawater was, in fact, much lower than the conventional drinking water with fresh source water.

Controlling disinfection byproducts from treated wastewater using adsorption with granular activated carbon: Impact of pre-ozonation and pre-chlorination

This study measured chlorine- and chloramine-reactive precursors using formation potential (FP) tests of nine U.S. Environmental Protection Agency (EPA) regulated and 57 unregulated disinfection byproducts (DBPs) in tertiary-filtered wastewater before and after pilot-scale granular activated carbon (GAC) adsorption. Using breakthrough of precursor concentration and of concentration associated calculated cytotoxicity and genotoxicity (by correlating known lethal concentrations reported elsewhere), the performance of three parallel GAC treatment trains were compared against tertiary-filtered wastewater: ozone/GAC, chlorine/GAC, and GAC alone. Results show GAC alone was the primary process, versus ozone or chlorine alone, to remove the largest fraction of total chlorine- and chloramine-reactive DBP precursors and calculated cytotoxicity and genotoxicity potencies. GAC with pre-ozonation removed the most chlorine- and chloramine-reactive DBP precursors followed by GAC with pre-chlorination and lastly GAC without pre-treatment. GAC with pre-ozonation produced an effluent with cytotoxicity and genotoxicity of DBPs from FP that generally matched that of GAC without pre-oxidation; meanwhile removal of toxicity was greater by GAC with pre-chlorination. The cytotoxicity and genotoxicity of DBPs from FP tests did not scale with DBP concentration; for example, more than 90% of the calculated cytotoxicity resulted from 20% of the DBPs, principally from haloacetaldehydes, haloacetamides, and haloacetonitriles. The calculated cytotoxicity and genotoxicity from DBPs associated with FP-chloramination were at times higher than with FP-chlorination though the concentration of DBPs was five times higher with FP-chlorination. The removal of DBP precursors using GAC based treatment was at least as effective as removal of DOC (except for halonitromethanes for GAC without pre-oxidation and with pre-chlorination), indicating DOC can be used as an indicator for DBP precursor adsorption efficacy. However, the DOC was not a good surrogate for total cytotoxicity and genotoxicity breakthrough behavior, therefore, unregulated DBPs could have negative health implications that are disconnected from general water quality parameters, such as DOC, and regulated classes of DBPs. Instead, cytotoxicity and genotoxicity correlate with the concentration of specific classes of unregulated DBPs.

SUN-241 Adult Exposure to Iodoacetic Acid Leads to Abnormal Expression of Key Genes Related to Hypothalamic and Pituitary Control of Reproductive Function

Water disinfection byproducts (DBPs) are formed when chemicals used to decontaminate water come into contact with natural or synthetic organic material. DBPs have been linked to a range of health concerns including reproductive disfunction. One such DBP, the monohalogenated iodoacetic acid (IAA), is formed when iodide reacts with a disinfectant, for example, chlorine. IAA is of particular health concern; not only is iodide widely present in the water supply, especially in coastal communities and those near fracking sites, but IAA has been found to be one of the most cyto- and genotoxic DBPs. Further, a previous study has indicated that in vitro IAA exposure significantly inhibits antral follicle growth and reduces estradiol levels in ovaries. However, little is known about how IAA affects the other major components of the reproductive axis: the hypothalamus and pituitary. The reproductive axis relies on homeostatic release of hormones to communicate from one organ to another and alterations at any level may impact reproduction. So, we set out to test the hypothesis that exposure to IAA would lead to disrupted expression of key hypothalamic and pituitary genes related to reproductive function. We continually exposed female adult CD1 mice to 0.5, 10, 100, or 500 mg/L IAA in their drinking water for approximately 35 days (postnatal day 40 (P40) to their first day in diestrus following P75.) Whole pituitaries and hypothalamic punches containing the arcuate nucleus (ARC), anteroventral periventricular zone (AVPV), and medial preoptic nucleus (mPOA) were collected and processed for qPCR analysis. We find that while kisspeptin (Kiss1) expression in the AVPV - the population responsible for generating the LH surge - is unchanged, 0.5 mg/L IAA exposure significantly increases Kiss1 in the ARC, which controls pulsatile GnRH release, and there is a trending increase (p=.056) at 10mg/L. We also measured ARC expression of Neurokinin B (NKB; Tac2), a neuropeptide secreted by kisspeptin co-expressing neurons to autosynaptically stimulate Kiss1 release. We found no change in mRNA levels of Tac2. We also saw no significant changes in GnRH (Gnrh1) mRNA expression. At the level of the pituitary, there is no change in Lhb mRNA levels. Exposure to 10 mg/L IAA leads to significantly reduced Fshb expression, however FSH serum levels are not significantly changed. These data, taken together with previous findings in the ovary, indicate that IAA has the potential to disrupt each major level of the reproductive axis: ovarian follicle development and steroid synthesis, hypothalamic arcuate Kiss1 synthesis, and Fshb synthesis from the pituitary. Further research is necessary to elucidate at which levels IAA acts directly and at which it acts through action on another component of the axis. Additionally, future studies can clarify the mechanism through which IAA has these effects.

The influence of the UV/chlorine advanced oxidation of natural organic matter for micropollutant degradation on the formation of DBPs and toxicity during post-chlorination

This study compares the influences of UV/chlorine and UV/H2O2 advanced oxidation of natural organic matter at the equivalent degradation of two model micropollutants on the formation of disinfection by-products (DBPs) and toxicity during post-chlorination. At 90% degradation of carbamazepine, the UV/chlorine advanced oxidation process (AOP) at pH 6.0 (3.0 mg/L chlorine and 280 mJ/cm2) resulted in comparable yields of dichloroacetic acid, trichloroacetic acid, chloroform, chloral hydrate, dichloroacetonitrile, trichloropropanone and total organic chlorine (TOCl) during the post-chlorination, compared to the UV/H2O2 AOP (8.0 mg/L H2O2 and 280 mJ/cm2). The UV/chlorine AOP increased the chloroacetic acid yields by 28–43% at pH 7.0 and 8.0. The cytotoxicity with the UV/chlorine AOP was 32% lower than with the UV/H2O2 AOP, however, the genotoxicity was similar. At the 90% degradation of atrazine, the UV/chlorine AOP (6.0–13.9 mg/L chlorine and 750–1000 mJ/cm2) increased the chloroacetic acid yields by 35–81% but did not increase the yields of other four known DBPs and TOCl, compared to the UV/H2O2 AOP (8.0–12.9 mg/L chlorine and 750–1000 mJ/cm2). The cytotoxicity and genotoxicity with the UV/chlorine AOP at pH 6.0 were 22–27% lower than those with the UV/H2O2 AOP, likely due to the selective destruction of the precursors of cytotoxic and genotoxic DBPs by RCS. The TOCl yields were positively correlated to the decreases in the specific UV absorbance at 254 nm and humic-like fluorescence. The TOCl yields exhibited a linear relationship with the genotoxicity (R2 = 0.81) but were weakly correlated with the cytotoxicity (R2 = 0.40). Although the UV/chlorine AOP increases the formation of some DBPs under certain circumstances, compared to the UV/H2O2 AOP, it does not enhance the genotoxicity and even decreases the cytotoxicity.

Genotoxicity of disinfection byproducts and disinfected waters: A review of recent literature

The presence of water disinfection byproducts (DBPs) in tap water, resulting from disinfection processes involving chlorination or chloramination, increases the mutagenicity of the water and may pose adverse health effects. The topic was reviewed by DeMarini and coworkers in 2007. Here, we review research on the genotoxicity of DBPs published since that time. Studies, primarily using the Salmonella mutagenicity assay, have continued to show that chlorination or chloramination of source waters results in finished, tap, or swimming pool/spa water that is more mutagenic than the original source water. The genotoxic potencies of DBPs in both bacterial and mammalian cells generally rank as iodinated > brominated > chlorinated. Several DBPs are genotoxic in vivo in plants as well as in animals such as the worm Caenorhabditis elegans and the zebrafish Danio rerio. Studies primarily using the comet assay in mammalian cells have identified several non-regulated DBPs as genotoxic. However, the comet assay detects DNA damage that is generally repaired by the cells; thus, genotoxicity data more relevant to persistent mutations, such as chromosomal or gene mutations, are needed for these DBPs. Recent molecular epidemiology has indicated that activation of brominated trihalomethanes by the enzyme GSTT1 and the lack of metabolism of haloacetic acids by a variant of enzyme GSTZ1 are likely causative mechanisms for bladder cancer associated with exposure to chlorinated water. Further studies, especially in vivo, are needed to determine the ability of various DBPs, especially unregulated ones, to induce both gene as well as chromosomal mutations. Such investigations, along with additional molecular epidemiology studies, are required for a comprehensive understanding of the genotoxic and carcinogenic risks associated with DBP exposure.

Genotoxicity Assessment of Drinking Water Disinfection Byproducts by DNA Damage and Repair Pathway Profiling Analysis.

Genotoxicity is considered a major concern for drinking water disinfection byproducts (DBPs). Of over 700 DBPs identified to date, only a small number has been assessed with limited information for DBP genotoxicity mechanism(s). In this study, we evaluated genotoxicity of 20 regulated and unregulated DBPs applying a quantitative toxicogenomics approach. We used GFP-fused yeast strains that examine protein expression profiling of 38 proteins indicative of all known DNA damage and repair pathways. The toxicogenomics assay detected genotoxicity potential of these DBPs that is consistent with conventional genotoxicity assays end points. Furthermore, the high-resolution, real-time pathway activation and protein expression profiling, in combination with clustering analysis, revealed molecular level details in the genotoxicity mechanisms among different DBPs and enabled classification of DBPs based on their distinct DNA damage effects and repair mechanisms. Oxidative DNA damage and base alkylation were confirmed to be the main molecular mechanisms of DBP genotoxicity. Initial exploration of QSAR modeling using moleular genotoxicity end points (PELI) suggested that genotoxicity of DBPs in this study was correlated with topological and quantum chemical descriptors. This study presents a toxicogenomics-based assay for fast and efficient mechanistic genotoxicity screening and assessment of a large number of DBPs. The results help to fill in the knowledge gap in the understanding of the molecular mechanisms of DBP genotoxicity.

A comparison of genotoxicity change in reclaimed wastewater from different disinfection processes

Effluents before disinfection from four wastewater reclamation plants were treated with chlorine (Cl2), ozone (O3), chlorine dioxide (ClO2), medium-pressure ultraviolet (MPUV) and four different combinations of the above, to evaluate the effect of disinfection processes on the genotoxicity removal by the SOS/umu test. Results showed that the genotoxicity increased after MPUV irradiation (10–100 mJ/cm2), but declined when adopting other disinfection processes. The effectiveness of genotoxicity reduction by five chemical disinfectants was identified as: O3 > pre-ozonation with Cl2 ≈ ClO2 > combination of ClO2 and Cl2 > Cl2. The sequential combination of MPUV, Cl2 and O3 reduced the genotoxicity to a level similar to the source water. The influence of differential disinfection process varied on iodinated wastewater, which is closely related to the competitive reactions between disinfectants, iodine and dissolved organic matters. The removal of genotoxic pollutants and the formation of genotoxic disinfection by-products are the two major factors that lead to the change in genotoxicity during disinfection.

Spatial variations in the occurrence of potentially genotoxic disinfection by-products in drinking water distribution systems in China

We investigated the occurrence of disinfection by-products (DBPs) with genotoxic potential in plant effluent and distribution water samples from four drinking water treatment plants in two Chinese cities using comprehensive two-dimensional gas chromatography–quadrupole mass spectrometry. We tested the samples for 37 DBPs with genotoxic potential, which we had previously identified and prioritized in water under controlled laboratory conditions. Thirty of these DBPs were found in the water samples at detection frequencies of between 10% and 100%, and at concentrations between 3.90 and 1.77 × 103 ng/L. Of the DBPs detected, the concentrations of 1,1,1-trichloropropan-2-one were highest, and ranged from 299 to 1.77 × 103 ng/L with an average of 796 ng/L. The concentrations of 6-chloro-2-N-propan-2-yl-1,3,5-triazine-2,4-diamine and 2,6-ditert-butylcyclohexa-2,5-diene-1,4-dione were also much higher, and ranged from 107 to 721 ng/L, and from 152 to 504 ng/L, respectively. Concentrations of 1,1,1-trichloropropan-2-one, 2-chloro-1-phenylethanone, 2,2-dichloro-1-phenylethanone and 6-chloro-2-N-propan-2-yl-1,3,5-triazine-2,4-diamine were highest at or near the treatment plants and decreased with increasing distance from the plants. Patterns in the concentrations of benzaldehyde, 2-phenylpropan-2-ol, and 1-methylnaphthalene differed between plants. The levels of DBPs such as 4-ethylbenzaldehyde, (E)-non-2-enal, and 1-phenylethanone were relatively constant within the distribution systems, even at the furthest sampling points (20 km < d < 30 km). A risk assessment showed that there was no risk to human health. It is, however, important to note that, because of limited availability of toxicity data, only five DBPs were evaluated in this study. The risks to health associated with exposure to the target potentially genotoxic DBPs should not be ignored because of their prolonged existence in drinking water.

Assessing the genotoxicity of two commonly occurring byproducts of water disinfection: Chloral hydrate and bromal hydrate

Water disinfection treatments result in the formation of disinfection byproducts (DBPs) that have been linked to adverse human health outcomes including higher incidence of bladder and colorectal cancer. However, data about the genotoxicity of DBPs is limited to only a small fraction of compounds. Chloral hydrate (CH) and bromal hydrate (BH) are two trihaloacetaldehydes commonly detected in disinfected waters, but little is known about their genotoxicity, especially BH.We investigated the genotoxicity of CH and BH using a test battery that includes three in vitro genotoxicity assays.We conducted the Ames test using Salmonella bacterial strains TA97a, TA98, TA100 and TA102, and the alkaline comet assay and the micronucleus test both using Chinese hamster ovary cells. We carried out the tests in the absence and presence of the metabolic fraction S9 mix.CH did not exhibit statistically significant genotoxic effects in any of the three assays. In contrast, BH exhibited mutagenic activity in the Salmonella strain TA100 and induced statistically significant DNA lesions in CHO cells as appeared in the comet assay. The genotoxic potential of BH in both assays decreased in the presence of the metabolic fraction S9 mix. BH did not induce chromosomal damage in CHO cells.Our results show that BH exhibited genotoxic activity by causing mutations and primary DNA damage while CH did not induce genotoxic effects. Our findings highlight concerns about the higher genotoxicity of brominated DBPs in comparison to their chlorinated analogues.

Granular Activated Carbon Treatment May Result in Higher Predicted Genotoxicity in the Presence of Bromide.

Certain unregulated disinfection byproducts (DBPs) are more of a health concern than regulated DBPs. Brominated species are typically more cytotoxic and genotoxic than their chlorinated analogs. The impact of granular activated carbon (GAC) on controlling the formation of regulated and selected unregulated DBPs following chlorine disinfection was evaluated. The predicted cyto- and genotoxicity of DBPs was calculated using published potencies based on the comet assay for Chinese hamster ovary cells (assesses the level of DNA strand breaks). Additionally, genotoxicity was measured using the SOS-Chromotest (detects DNA-damaging agents). The class sum concentrations of trihalomethanes, haloacetic acids, and unregulated DBPs, and the SOS genotoxicity followed the breakthrough of dissolved organic carbon (DOC), however the formation of brominated species did not. The bromide/DOC ratio was higher than the influent through much of the breakthrough curve (GAC does not remove bromide), which resulted in elevated brominated DBP concentrations in the effluent. Based on the potency of the haloacetonitriles and halonitromethanes, these nitrogen-containing DBPs were the driving agents of the predicted genotoxicity. GAC treatment of drinking or reclaimed waters with appreciable levels of bromide and dissolved organic nitrogen may not control the formation of unregulated DBPs with higher genotoxicity potencies.

Comparative cytotoxic and genotoxic potential of 13 drinking water disinfection by-products using a microplate-based cytotoxicity assay and a developed SOS/umu assay.

The implications of disinfection by-products (DBPs) present in drinking water are of public health concern because of their potential mutagenic, carcinogenic and other toxic effects on humans. In this study, we selected 13 main DBPs found in drinking water to quantitatively analyse their cytotoxicity and genotoxicity using a microplate-based cytotoxicity assay and a developed SOS/umu assay in Salmonella typhimurium TA1535/pSK1002. With the developed SOS/umu test, eight DBPs: 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-fura3-chloro-4-(dichloromethyl)-5-hydroxy-2-[5H]-furanone (MX), dibromoacetonitrile (DBN), iodoacetic acid (IA), bromochloroacetonitrile (BCN), bromoacetic acid (BA), trichloroacetonitrile (TCN), dibromoacetic acid (DBA) and dichloroacetic acid (DCA) were significantly genotoxic to S. typhimurium. Three DBPs: chloroacetic acid (CA), trichloroacetic acid (TCA) and dichloroacetonitrile (DCN) were weakly genotoxic, whereas the remaining DBPs: chloroacetonitrile (CN) and chloral hydrate (CH) were negative. The rank order in decreasing genotoxicity was as follows: MX > DBN > IA > BCN > BA > TCN > DBA > DCA > CA, TCA, DCN > CN, CH. MX was approximately 370 000 times more genotoxic than DCA. In the microplate-based cytotoxicity assay, cytotoxic potencies of the 13 DBPs were compared and ranked in decreasing order as follows: MX > IA > DBN > BCN > BA > TCN > DCN > CA > DCA > DBA > CN > TCA > CH. MX was approximately 19 200 times more cytotoxic than CH. A statistically significant correlation was found between cytotoxicity and genotoxicity of the 13 DBPs in S. typhimurium. Results suggest that microplate-based cytotoxicity assay and the developed SOS/umu assay are feasible tools for analysing the cytotoxicity and genotoxicity of DBPs, particularly for comparing their toxic intensities quantitatively.

Genotoxicity of disinfection by-products (DBPs) upon chlorination of nine different freshwater algal species at variable reaction time

Nine local dominant freshwater algal species, including green algae ( Chlorella sp., Chlamydomonas sp. and Scenedesmus quadricauda ), diatom ( Navicula pelliculosa , Nitzschia palea Grunow and Synedra sp.), blue-green algae ( Microcystis sp., Chroococcus sp. and Gloeocapsa sp.) were isolated from source water reservoirs and cultivated in the laboratory. The algal biomass was chlorinated (20 °C, pH 7, residual chlorine 2 mg L −1 ). Yields of chloroform, dichloroacetic acid, trichloroacetic acid, dichloroacetonitrile and trichloroacetonitrile and genotoxicity of the chlorinated solutions at eight chlorination intervals (0.5, 1, 2, 5, 10, 30, 60 and 120 min) were determined via SOS-ChromoTest and Comet assay. The results showed that green algae and diatom were more effective disinfection by-products (DBPs) precursors than blue-green algae. Genotoxicity was shown to be chlorination time-dependent, in agreement with our previous findings, suggesting that intermediate DBPs rather than trihalomethanes or haloacetic acids were major contributors to the genotoxicity of chlorinated solutions.

Cytotoxicity analysis of water disinfection byproducts with a micro-pillar microfluidic device

Water disinfection byproducts (DBPs) are a class of chemicals that are produced when chemical disinfectants react with organic materials in untreated water. Cytotoxicity and genotoxicity of DBPs have been systematically evaluated to compile a comparative, quantitative database of in vitro mammalian cell toxicity of DBPs. However, one of the most challenging limitations for current DBP cytotoxicity assessment assays is sample availability. Although our current cytotoxicity assay using a 96-well microplate has been designed to reduce sample consumption, further minimization of the size of the test system would allow us to explore various possibilities for point-of-care applications. We have developed a microfluidic device with micro-pillars that shows high uniformity in distribution of cells across all chambers with low cell count. We compare the performance between the 96-well microplate and the microfluidic device by running 72-hour standalone-on-chip cell culture and cytotoxicity analysis experiments, using dimethyl sulfoxide (DMSO) and ethanol as model toxic agents, and bromoacetic acid (BAA) as a representative DBP. The results show close agreement between the two systems. The measured LC(50) values for the 96-well microplate and the microfluidic device are 1.54% v/v and 1.27% v/v for DMSO, 1.44% v/v and 2.92% v/v for ethanol, and 17.6 μM and 8.20 μM for BAA, respectively. The micro-pillar microfluidic device offers a great reduction in sample consumption while maintaining the accuracy of the cytotoxicity analyses of water disinfection byproducts.

Comparison of DNA damage in human-derived hepatoma line (HepG2) exposed to the fifteen drinking water disinfection byproducts using the single cell gel electrophoresis assay

Disinfection of drinking water reduces pathogenic infection, but generates disinfection by-products (DBPs) in drinking water. In this study, the effect of fifteen DBPs on DNA damage in human-derived hepatoma line (HepG2) was investigated by the single cell gel electrophoresis (SCGE) assay. These fifteen DBPs are: four trihalomethanes (THMs), six haloacetic acides (HAAs), three haloacetonitriles (HANs), 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), and chloral hydrate (CH). Based on the minimal effective concentration (MEC) at which DBPs induced significant increase in olive tail moment (OTM), the rank order of DNA-damaging potency is: bromodichloromethane (BDCM) > dibromochloromethane (DBCM) > tribromomethane (TBM) > trichloromethane (TCM) of the four THMs; iodoacetic acid (IA) > bromoacetic acid (BA) > dibromoacetic acid (DBA) > dichloracetic acid (DCA) > trichloroacetic acid (TCA) of the five HAAs; dibromoacetonitrile (DBN) ≈ dichloroacetonitrile (DCN) > trichloroacetonitrile (TCN) of the three HANs. The DNA damaging potency of MX and CH is similar to TCA and DCA, respectively. IA is the most genotoxic DBP in the fifteen DBPs, followed by BA. Chloroacetic acid (CA) is not genotoxic in this assay. Our findings indicated that HepG2/SCGE is a sensitive tool to evaluate the genotoxicity of DBPs and iodinated DBPs are more genotoxic than brominated DBPs, but chlorinated DBPs are less genotoxic than brominated DBPs.

Removal of genotoxicity in chlorinated secondary effluent of a domestic wastewater treatment plant during dechlorination

Dechlorination with tetravalent sulfur is widely used in wastewater treatment processes after chlorination. Dechlorination can remove certain genotoxic disinfection by-products (DBPs). However, the reactions occurring during dechlorination of chlorinated secondary effluent and their genotoxic chemicals are still very complex, and the related genotoxicity changes remain unknown. Therefore, the effects of dechlorination on genotoxicity in secondary effluent and its fractions and typical genotoxic chemical after chlorination were evaluated. The dissolved organic matter in the secondary effluent sample was separated into four fractions with XAD-8 resin. Genotoxicity of secondary effluent and its fractions was evaluated by SOS/umu test, an ISO standard method. The concentration of typical genotoxic chemical named ofloxacin was determined by liquid chromatography with a mass spectrometer and a fluorescence detector. Dechlorination with the addition of Na(2)SO(3) notably decreased the genotoxicity in the chlorinated secondary effluent, especially in the presence of high ammonia nitrogen concentration in the sample before chlorination. The Na(2)SO(3) addition significantly decreased the genotoxicity of the secondary effluent and its genotoxic ofloxacin prior to chlorination. The genotoxicity in the fractions containing hydrophobic acids (HOA) increased after chlorination, while addition of Na(2)SO(3) decreased the genotoxicity induced by chlorination. Tryptophan found in HOA exhibited genotoxicity after chlorination, while dechlorination decreased the genotoxicity in chlorinated tryptophan induced by DBPs. Dechlorination was found to decrease the genotoxicity of chlorinated secondary effluent. The decrease was associated with the reduction of genotoxicity in genotoxic chemicals in secondary effluent prior to chlorination and DBPs.

Genotoxicity and cytotoxicity assessment in lake drinking water produced in a treatment plant.

Chemical analyses and short-term mutagenicity bioassays have revealed the presence of genotoxic disinfection by-products in drinking water. In this study, the influence of the different steps of surface water treatment on drinking water mutagen content was evaluated. Four different samples were collected at a full-scale treatment plant: raw lake water (A), water after pre-disinfection with chlorine dioxide and coagulation (B), water after pre-disinfection, coagulation and granular activated carbon filtration (C) and tap water after post-disinfection with chlorine dioxide just before its distribution (D). Water samples, concentrated by solid phase adsorption on silica C18 columns, were tested in human leukocytes and HepG2 hepatoma cells using the comet assay and in HepG2 cells in the micronuclei test. A significant increase in DNA migration was observed in both cell types after 1 h treatment with filtered and tap water, and, to a lesser extent, chlorine dioxide pre-disinfected water. Similar findings were observed for the induction of "ghost" cells. Overloading of the carbon filter, with a consequent peak release, might explain the high genotoxicity found in water samples C and D. Cell toxicity and DNA damage increases were also detected in metabolically competent HepG2 cells treated with a lower concentration of tap water extract for a longer exposure time (24 h). None of the water extracts significantly increased micronuclei frequencies. Our monitoring approach appears to be able to detect contamination related to the different treatment stages before drinking water consumption and the results suggest the importance of improving the technologies for drinking water treatment to prevent human exposure to potential genotoxic compounds.

A new approach to evaluating the toxicity and genotoxicity of disinfected drinking water

The aim of this study was to evaluate the formation of toxic and genotoxic compounds in surface drinking waters treated with two widely used disinfectants, sodium hypochlorite (NaClO) and chlorine dioxide (ClO2), and a new disinfectant, peracetic acid (PAA). For this purpose a pilot plant was set up to add these biocides continuously to pre-filtered lake water flowing into three different basins. During three seasonal experiments, short-term in vivo tests (with plant, fish and molluscs) and in vitro tests (with bacteria, yeast and human cells) were carried out to evaluate the formation of genotoxic disinfection by-products (DBPs). Gas chromatography/mass spectrometry (GC/MS) was used to identify DBPs produced during the different treatments, microbiological analyses were performed to test the biocidal activity of the disinfectants, and chemical analyses were carried out to evaluate the quality of the water. The pilot drinking water plant under study was useful in studying the toxicity and genotoxicity of disinfected drinking water with this combined chemical/biotoxicological approach. This paper describes the setting up of the pilot plant and sets out/reports the results of the microbiological and chemical analyses.

Potent inhibition of gap junctional intercellular communication by 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5 H)-furanone (MX) in BALB/c 3T3 cells

The chlorohydroxyfuranones (CHFs) MX [3-chloro-4-(dichloromethyl)-5-hydroxy-2(5 H)-furanone], MCA [3,4-dichloro-5-hydroxy-2(5 H)-furanone], CMCF [3-chloro-4-(chloromethyl)-5-hydroxy-2(5 H)-furanone], and MCF [3-chloro-4-methyl-5-hydroxy-2(5 H)-furanone] are genotoxic disinfection by-products of drinking water chlorination. MX, MCA, and MCF also promote foci formation in the two-stage cell transformation assay. The cellular mechanisms underlying this apparent promotional effect are not known. In the present study, the effects of MX, MCA, CMCF, and MCF on gap junctional intercellular communication (GJIC) were measured in BALB/c 3T3 cells using the scrape loading dye technique. The effect of MX on apoptosis in the same cell line was explored by assaying caspase-3-like protease activity. All the four CHFs inhibited GJIC after 30 min exposure in a dose-dependent fashion but there was a marked difference in the ranges of their active concentrations. MX was almost as potent an inhibitor of GJIC (inhibition at nanomolar concentrations) as 12- O-tetradecanoylphorbol-13-acetate (TPA) (positive control), while MCA was 10 times weaker, CMCF 10,000 times weaker, and MCF 20,000 times weaker than MX. After prolonged exposure periods (up to 6 h), GJIC recovered somewhat upon MX and MCA exposures, the inhibition of GJIC by MCF remained constant but CMCF showed an irreversible increasing inhibitory effect. MX caused apoptosis as a “window” effect at concentrations 2000–4000-fold higher than those needed to inhibit GJIC. The results indicate that MX is a potent inhibitor of GJIC in BALB/c 3T3 cells and this inhibition might be one mechanism by which MX can promote malignant foci formation. MCA also has a specific potential to inhibit GJIC whereas MCF and CMCF affected GJIC at concentrations, similar to those evoking genotoxicity in vitro.